Method of Preparing and Using a Drag-Reducing Additive Having a Dispersion Polymer

ABSTRACT

A method begins with the step of preparing a drag-reducing additive by mixing a dispersion polymer with a surfactant and a solvent. The method continues with the step of forming a drag-reducing composition by combining the drag-reducing additive with an aqueous treatment fluid. The method further involves the step of injecting the drag-reducing composition into a subterranean formation, a pipeline or a gathering line.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/907,226 filed Feb. 27, 2018 entitled, “Method of Preparing and UsingDrag-Reducing Dispersion Polymer Compositions,” which is a division ofU.S. patent application Ser. No. 14/323,830 entitled “Drag-ReducingCopolymer Compositions,” filed Jul. 3, 2014, which is now abandoned,which is a continuation of U.S. patent application Ser. No. 12/268,408,entitled “Drag-Reducing Copolymer Compositions,” filed Nov. 10, 2008,which is now U.S. Pat. No. 8,865,632, the disclosures of which areherein incorporated by reference.

FIELD OF THE INVENTION

The present invention is generally related to the treatment of oil andgas wells and/or gathering lines and pipelines, and more particularlyrelated to a composition and process for reducing the drag, or fluidfriction, caused by the injection of aqueous treatment fluids intosubterranean geological formations.

BACKGROUND OF THE INVENTION

Crude oil and natural gas are typically recovered from subterraneanreservoirs through the use of drilled wells and production equipment.After the wells are drilled, cased and cemented, it is often necessaryto stimulate the reservoir by means of hydraulic fracturing or acidizingto achieve economical flow of gas and oil. This typically requirespumping an aqueous treatment fluid into the well at high rates, so thatthe fluid will build up pressure and cause the formation to fracture.

In the process of pumping, substantial fluid friction pressure, or drag,is observed between the treatment fluid and the tubing or casing as thefluid reaches turbulent flow, thus causing a substantial energy loss. Asa result of the energy loss, a higher pumping pressure is needed toachieve the desired flow rate and pressure. It is therefore common toinclude drag-reducing additives in the aqueous treatment fluids tosuppress the turbulence and realize lower pumping pressures. Commondrag-reducing additives include oil-external emulsions of polymers withoil-based solvents and an emulsion-stabilizing surfactant. The emulsionsmay include guar-based or polyacrylamide-acrylic acid (PAM-AA)copolymers. Typically these prior art emulsions consist of an aqueousphase dispersed in a non-aqueous phase, in a weight ratio of from about5:1 to about 10:1 aqueous phase to non-aqueous phase.

The surfactants in known drag reduction emulsions are typicallyemulsifying surfactants that stabilize the emulsions. The emulsifyingsurfactants have low HLB values, generally between 4 and 8. The transferof the polymer from inside the aqueous phase of the oil-externalemulsion into an aqueous treatment fluid is achieved by the inversion ofan emulsion. A common way to achieve this inversion is to use aninverting surfactant, which is typically water-soluble and has an HLB ofgreater than about 7. Inverting surfactants may be a part of polymeremulsion formulations or may be added to a solution into which theemulsion is to be inverted.

The problem encountered with these known treatments, however, is thatinverting surfactants may adversely interact with the emulsifier oremulsion and destroy it prior to use. Thus, commercially availablepolymer emulsions generally contain less than 5% of invertingsurfactant. Polymer emulsions with this low amount of invertingsurfactant, however, may not provide the desired reduction in frictionbecause the polymer emulsion either does not invert completely or is notbrine or acid tolerant.

In the event that acid or high salt contents are encountered, emulsioncopolymers of 2-Acrylamido-2-methyl propane sulfonic acid (AMPS) arecommonly used. These AMPS copolymers, however, may be cost prohibitive.In either case, the high molecular weight polymers may also causesubstantial damage to the formation permeability. Thus, there is acontinued need for more effective compounds that are more efficient,more salt tolerant, and less damaging.

SUMMARY OF THE INVENTION

In one embodiment, the present invention includes a method that beginswith the step of preparing a drag-reducing additive by mixing adispersion polymer with a surfactant and a solvent. The method continueswith the step of forming a drag-reducing composition by combining thedrag-reducing additive with an aqueous treatment fluid. The methodfurther involves the step of injecting the drag-reducing compositioninto a subterranean formation, a pipeline or a gathering line.

In another embodiment, the present invention includes a method thatbegins with the step of preparing a drag-reducing additive by mixing40-85% by weight of a dispersion polymer with 10-35% by weight of asurfactant with an HLB greater than about 8 and 5-30% by weight of asolvent. The method continues with the step of forming a drag-reducingcomposition by combining the drag-reducing additive with an aqueoustreatment fluid. The method also includes the step of injecting thedrag-reducing composition into a subterranean formation, a pipeline or agathering line.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to the preparation and use of a polymercomposition that can be used as a drag-reducing additive. Unlike priorart drag reducers, the additives of the preferred embodiments are formedby the combination of polymer with relatively high amount of surfactant.In a first embodiment, a three-component additive is formed upon thecombination of a polymer and a surfactant with a solvent. In analternate embodiment, a two-component additive is formed upon acombination of a polymer and a surfactant. It is understood that thecompositions of these embodiments have a variety of uses, one of whichis drag reduction. The solvent is preferably a terpene. The additivescan be added to an appropriate treatment fluid to form a well treatmentcomposition or a composition for treatment of gathering lines orpipelines.

In a preferred embodiment, the polymer component of the additive is inthe form of a commercially-available polymer emulsion, which typicallyalready includes some solvent and emulsion surfactant. However, polymeremulsion could be synthesized, instead of purchased. It will beunderstood that the term “polymer” includes both homopolymers andcopolymers. Upon addition to the treatment fluid, the components of thedrag-reducing additive form an oil-in-water emulsion that reduces thefriction between the turbulent flow of the treatment fluid and the wallsof the well tubing or casing, or the walls of a pipeline or gatheringline. In a preferred embodiment, the treatment fluid is water-based.Upon dilution, the additive may form a microemulsion, a miniemulsion, ananoemulsion or an emulsion.

By adding a relatively large amount of surfactant to the additive,compared to surfactant levels in prior art friction reducers, thehydrophilicity and dispersibility of the polymer is increased, thusincreasing the stability of the system in aqueous downhole fluid or in apipeline or gathering lines. Furthermore, the increased surfactant levelincreases the inversion rate of the additive, even under low energyconditions. As a result, less polymer is needed to achieve the desiredfriction-reducing performance, which results in less damage downhole.Another benefit of the increased surfactant level in the additive isimproved performance in brine.

The first component in the system, the polymer, may be nonionic,zwitterionic, anionic, or cationic. The polymer may further be adispersion polymer or an emulsion polymer. Such polymer preferablyconsists of acrylamide present in the amount between 1 and 100 mole %and cationic, anionic, zwitterionic, or nonionic monomers present in theamount between 0 and 99 mole %.

When the copolymer includes acrylamide and an anionic monomer, theanionic monomer may be acrylamidopropanesulfonic acid, acrylic acid,methacrylic acid, monoacryloxyethyl phosphate, or their alkali metalsalts. When the copolymer includes acrylamide and a cationic monomer,the cationic monomer may be dimethylaminoethylacrylate methyl chloridequarternary salt, diallyldimethylammonium chloride (DADMAC),(3-acrylamidopropyl)trimethylammonium chloride (MAPTAC),(3-methacrylamido)propyltrimethylammonium chloride,dimethylaminoethyl-methacrylate methyl chloride quarternary salt, ordimethylaminoethylacrylate benzylchloride quarternary salt.

When the copolymer includes acrylamide and a nonionic monomer, thenonionic monomer may be acrylamide, methacrylamide, N-methylacrylamide,N,N-dimethyl(meth)acrylamide, octyl acrylamide,N(2-hydroxypropyl)methacrylamide, N-methylolacrylamide,N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide,poly(ethylene glycol)(meth)acrylate, poly(ethylene glycol) monomethylether mono(meth)acrylate, N-vinyl-2-pyrrolidone, glycerolmono((meth)acrylate, 2-hydroxyethyl (meth)acrylate, vinyl methylsulfone,or vinyl acetate.

When the copolymer includes acrylamide and a zwitterionic monomer, thezwitterionic monomer may be selected from those described in U.S. Pat.No. 6,709,551 or be selected fromN,N-dimethyl-N-acryloyloxyethynyl-N-(3-sulfopropyl)-ammonium betaine,N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine,N,N-dimethyl-N-methacrylcryloyloxyethynyl-N-(3-sulfopropyl)-ammoniumbetaine,N,N-dimethyl-N-methacrylcryloyloxyethynyl-N-(3-sulfopropyl)-sulfoneumbetaine, 2-(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfoniumbetaine, 2-[(2-acryloylethyl)dimethylammonio]ethyl 2-methyl phosphate,2-(acryloyloxyethyl)-2′-(trimethylammonium)ethyl phosphate, or[(2-acryloylethyl)dimethylammonio]methyl phosphonic acid. It will beunderstood that the lists of potential monomers are not limiting, andthe use of other monomers may also be appropriate.

From testing of various polymers in the three-component additiveembodiment, it was determined that the use of a copolymer made up ofpolyacrylamide and an anionic monomer additive resulted in increasedpermeability restoration when compared to copolymers with nonionic orcationic monomers. Thus, it is preferred to use a copolymer ofacrylamide and an anionic monomer, such as acrylic acid. In a presentlypreferred embodiment, the copolymer is a polyacrylamide-acrylic acid(PAM-AA) copolymer having a molecular weight from about 4 million to 20million amu, with a percentage of acrylamide in the range of 60-99% byweight and a percentage of acrylic acid from 1 to 40% by weight.

The second component in the three component additive embodiment, thesurfactant, may have a hydrophile-lipophile balance (HLB) of above about7, and preferably has an HLB of between 11 and 15. It will be understoodthat the surfactant component may be made up of one surfactant or ablend of surfactants. Highly preferred nonionic surfactants have an HLBof 12 to 13. These surfactants aid in the inversion of the polymer whenthe additive comes into contact with aqueous treatment fluid, and aresometimes referred to as inverting surfactants. Preferred surfactantsare liquids chosen from ethoxylated glycerides, ethoxylated sorbitanesters, ethoxylated alkyl phenols, ethoxylated alcohols, castor oilethoxylates, cocoamide ethoxylates, and sorbitan monooleates such aspolyoxyethylene 20 sorbitan monooleate (Tween® 80). In a particularlypreferred embodiment, the surfactant is a castor oil ethoxylate with 30moles of ethylene oxide (EO) per 1 mole of castor oil ethoxylate. In analternate particularity preferred embodiment, the surfactant componentis a surfactant mixture of: (i) alcohol ethoxylate C8-C18 with 5-20moles EO; and (ii) ethoxylated castor oil with 25-45 moles of EO.

The third component in the three-component additive embodiment, thesolvent, is preferably a blend of naturally occurring plant terpenes.Terpenes often consist of units of isoprene and have the formula(C₅H₈)_(n), where n is the number of linked isoprene units. Otherterpenes, such as those found in eucalyptus and peppermint oils, mayinclude compounds containing oxygen. A complex plant-derived terpenetypically includes a variety of compounds, including monoterpenes(C₁₀H₁₆), d-limonene, dipentene, 1-limonene, d,l-limonene, myrcene, andα-pinene. Additional terpenes include terpinolene, β-pinene, eucalyptol,α-terpineol, β-terpineol, sabinene, menthofurane, 1,8-cineole,citronellal, cintronellol, menthol, mentohone, and alcohols andaldehydes of the same composition and mixtures thereof.

The terpene blend may be further combined with other solvents such asother plant-derived alcohols or esters, or aromatic hydrocarbons.Plant-derived alcohols in the solvent may include terpenoids andstraight chain alcohols with the formula CH₃(CH₂)_(n)OH, where n≥9 or11. Plant-derived esters include methyl and ethyl esters ofnaturally-occurring oils such as cottonseed or soybean oil. It should benoted that synthetic solvents can also be used as the solvent phase.

In a preferred embodiment, the solvent has a KB (Kauri-butanol) value ofgreater than about 60. Preferred terpenes are those derived from citrusfruits, eucalyptus, or mint. In a particularly preferred embodiment, thesolvent is a biodegradable solvent blend primarily made up ofd-limonene.

Emulsion polymers that comprise a component of the present additive canbe either obtained from commercial suppliers or be synthesized. In apreferred embodiment, a drag-reducing additive is made by mixing about40 to 85% by weight of a commercially available polymer emulsion, suchas the type available from Hychem, Inc., with about 5 to 30% by weightadditional solvent and about 5 to 35% by weight of additionalsurfactant. The commercially available polymer emulsion may include apolymer and small amounts of an emulsion surfactant, a solvent, andpossibly an inverting surfactant. Thus, the additional solvent that isadded to the polymer emulsion will be referred to as the second solvent,and the additional surfactant that is added to the polymer emulsion willbe referred to as the second surfactant.

In a particularly preferred embodiment, the three-componentdrag-reducing additive is prepared by blending about 55 to 65% by weightof a commercially available polymer emulsion with about 10 to 30% byweight of a second terpene solvent and about 20% to 35% by weight of asecond nonionic surfactant. In this preferred embodiment, the secondnonionic surfactant is made up primarily of a surfactant with an HLB of12 to 13, such as a castor oil ethoxylate with 30 moles of ethyleneoxide. The commercially available polymer emulsion preferably includesacrylamide in the range of 60 to 90% by weight and acrylic acid in therange of 5 to 30% by weight. It is preferred to mix the additionalsurfactant and solvent before adding the polymer emulsion, but order ofmixing is not critical. In other preferred embodiments, thedrag-reducing additive includes other additives such as acids, bases,corrosion inhibitors, proppants, biocides, oxygen scavengers, asphalteneinhibitors, and oils.

In another embodiment, three-component drag-reducing additive is formedby synthesizing a polymer emulsion that is combined with the secondterpene solvent and second surfactant, instead of using a commerciallyavailable polymer emulsion. The synthesized polymer emulsion is combinedwith the second solvent and second surfactant in the amounts describedabove. Methods suitable for preparation of emulsion polymers are wellknown to those skilled in the art. For example, such methods aredescribed in U.S. Pat. Nos. 3,284,393; 3,734,873; 6,605,674; and6,753,388. Suitable emulsion polymers can be prepared by a process thattypically involves preparing an oil phase containing suitablesurfactants, preparing an aqueous monomer phase containing the monomers,preparing a water-in-oil emulsion of the aqueous phase in the oil phase,and performing polymerization of monomers, usually by means of freeradical polymerization. In certain instances structural modifiers orcrosslinking agents can be added at various stages of the process.Suitable such agents and means of their addition would be known to thoseskilled in the art. Polymer solids in the prepared emulsion polymerstypically comprise from about 5 to about 60% by weight. It should beunderstood, however, that there may be other methods of preparing thesuitable polymer emulsion.

Friction reducing polymers suitable to practice the present inventionmay also be chosen from a class of dispersion polymers, such as thosedescribed in U.S. Pat. Nos. 4,929,655; 5,605,970; 5,837,776; 5,597,858;6,217,778; 6,365,052; 7,323,510; and European patent EP630,909. Use ofdispersion polymers for reducing friction has been disclosed in U.S.Pat. No. 6,787,506. Dispersion polymers may either be acquired from acommercial source or synthesized. Typical synthesis of dispersionpolymers involves polymerizing one or more water-soluble monomers in anaqueous reaction mixture, wherein the aqueous reaction mixture containsa water soluble salt, at least one polymeric dispersant, optionallycontains an organic alcohol, optionally contains a pre-formed polymerseed. The water soluble polymer formed as a result of polymerization isinsoluble in the aqueous reaction mixture at the concentration thereofformed during the polymerization. Polymer solids in the prepareddispersion are typically from about 5% to about 60% by weight.

Dry (powder) polymers may be used as part of this additive if they arefirst dissolved in a treatment fluid miscible with water or as adispersion. Other drag reducing polymers such as guar, xanthan, andother natural polymers along with synthetics can also be used in thepractice of this invention.

When combined, the blend of the copolymer, solvent, and surfactantbecomes a one phase system that may remain stable for more than 24 hoursand may be adapted for use in a broad temperature range. Thus, each ofthe selected components in the drag-reducing additive may be mixedtogether before delivery to the well.

A two-component embodiment of the additive is preferably made bycombining about 50-99% of a polymer emulsion with about 1-50% of asurfactant with an HLB above about 7. Having more than 50% surfactantmay also yield suitable friction reducing formulations, but such systemsmay be unstable, not as effective and efficient in friction reduction,and not as cost-advantageous, as systems with less than 50% surfactant.The two-component additive becomes highly viscous when about 75-99% ofthe polymer emulsion is combined with about 1-25% of the surfactant.Addition of less than 5% of a solvent may result in producing highviscosity embodiment of the additive. Addition of a small amount ofsolvent may actually increase the viscosity of the additive, but uponaddition of larger amounts of solvent, the viscosity will be decreased.In another embodiment, less than about 30% of the polymer emulsion iscombined with about 70-99% of the surfactant with an HLB of above about7. In a preferred embodiment, the two-component additive may be made byusing a commercially available polymer emulsion, and the surfactant withan HLB of greater than about 7, and most preferably with an HLB of 12 to13. The highly viscous form of the two-component additive may bedelivered to a solution by a pump, extruding device or any othersuitable means. The highly viscous form of the two-component additivemay generally have a complex viscosity magnitude of greater than about40 Pascal-sec (Pa s).

The additives described above have multiple uses. The uses may include,without limitation, drag reduction, flocculation, water clarification,solids/liquids separation, sludge dewatering, mining, and papermaking.

More specifically, compositions described above may be suitable asflocculation-promoting agents in solids-liquid separation, watertreatment, papermaking, mining, and other applications. They can be usedalone, or in a combination with various other additives typically usedto promote flocculation. These other additives include but not limitedto high molecular weight polymers bearing anionic and cationic charge orno charge at all. Some non-limiting examples of such polymers includevarious co-polymers of polyacrylamide, cross-linked, linear or branched,as well as polyethylene oxide and poly naphthalene sulfonate. Otherknown additives in the flocculation process that can be used incombination with the compositions of the present invention includechemically modified and unmodified polysaccharides, such as starches,coagulants, such as aluminum sulfate, poly aluminium chloride,poly-diallyl dimethyl ammonium chloride (DADMAC), poly-epichlorohydrinedimethyl ammonium chloride, 3-trimethylammonium propyl methacrylamidechloride (MAPTAC), or other similar substances. Other suitable additivescan be chosen from a class of colloidal materials, such as colloidalsilica, colloidal borosilicate, colloidal zirconium oxide, colloidalaluminum oxide and hydroxide, colloidal alumosilicate, or clays, bothnaturally occurring and synthetic, such as bentonite, laponite,saponite. Microgels, such as polysilicate microgel and polyalumosilicatemicrogel, are also suitable colloidal products. Structurally rigidpolymers and polymer microbeads also may be used in combination withcompositions of the present invention.

At the well site or in the pipelines or gathering lines, thedrag-reducing additive is added to a water-based treatment fluid to bepumped downhole or through the piping system. In a preferred embodiment,the drag-reducing additive comprises about 0.05 to 2 gallons of solutionper 1000 gallons of water (gpt).

In a presently preferred embodiment, the drag-reducing additive isdelivered downhole or into a pipeline or gathering line by continuouslyadding it to the water-based treatment fluid as the treatment fluid ispumped, at rates of 0.05 to 5 gallons drag-reducing additive per 1000gallons fracturing fluid. The drag-reducing additive is preferably addedto the treatment fluid at or near the blending device and before thehigh pressure pumps in a fracturing treatment. In a friction-reducingapplication, the emulsion inverts rapidly as the fracturing fluidproceeds down the tubulars, allowing the copolymer solution tosolubilize in the aqueous phase. The drag-reducing additive suppressesturbulence and lowers the necessary pumping pressure.

The following examples describe tests performed on various embodimentsof the additive, as well as prior art drag-reducing systems. It will beunderstood that these examples are merely illustrative and are not to beconsidered limiting.

Testing

Friction loop devices to evaluate friction/drag reduction are known inthe art. The device used to for the following tests consists of a 15gallon tank from which fluid is pumped at a maximum flow rate of 12gallons per minute (gpm) through a series of pipes. The first pipe is a10 feet long with a 0.75 inch outer diameter (OD) and a 0.62 inch innerdiameter (ID). The first pipe is connected to a 25 foot long, 0.50 inchOD, 0.40 inch ID stainless steel test pipe. Differential pressure ismeasured by means of pressure transducers across a 10 foot section ofthe test pipe called the “Test Section.” The Test Section begins at apoint 10 feet along the test pipe. After the fluid flows through theTest Section, it is looped back into the pump. The output of thedifferential pressure measurements is registered by a computer runningLabVIEW automation software available from the National InstrumentsCorporation. It will be understood that other methods of testing dragreduction may be used.

In a typical experiment a 15 gallon reservoir is filled with 8 gallonsof base fluid comprising either tap water or brine, which will provide abaseline and to verify proper operation of the flow loop. The base fluidcan also be produced water from a well or other process water. Onesuitable brine consists of 7% by weight potassium chloride solution. Thebase fluid is recirculated for 2 minutes at a flow rate of 10 gpm, thebaseline point is recorded, and the flow loop is then stopped. Thedrag-reducing additive or prior art drag reducer is then injected usinga 60 ml syringe at doses between 0.05 to 2 gpt. The fluid is thenrecirculated in the loop. The flow rate initially is set at 12 gpm andthen ramped down to 2 gpm in 2 gpm increments. At each flow rate thefluid is recirculated for 60 seconds. After 2 gpm flow rate has beenreached, the flow rate is ramped back to 12 gpm in 2 gpm increments.This part of test is referred to as “ramping.” After the last 12 gpmsetting is reached, the flow rate is reduced to 10 gpm and the liquid isallowed to further recirculate in the loop for 10 minutes. This part ofexperiment is referred to as “recirculation.” During recirculationdifferential pressure is measured at the beginning (t=0) and at the end(t=10 min) of the process. Performing the drag reduction experiment insuch way allows one to simulate situations of changing flow rategradients typically encountered in the oilfield, such as in performinghydraulic fracturing jobs. The percent friction reduction (% FR) iscalculated at each flow rate as follows:

${\% \mspace{14mu} {FR}} = {\frac{{DP}_{BL} - {DP}_{S}}{{DP}_{BL}} \times 100\; \%}$

where DP_(BL) and DP_(S) are the differential pressures obtained withoutand with drag reducing system, respectively. The value of DP_(BL)represents 100% friction baseline for water or brine.

At each flow rate, the value of DP_(BL) is calculated using thefollowing set of equations:

${\Delta \; P_{BL}} = \frac{L \times v \times \rho \times f}{25.8 \times D}$$v = \frac{Q}{2.45 \times D^{2}}$$f = {\frac{0.3164}{4} \times {Re}^{0.25}}$${Re} = \frac{928 \times D \times v \times \rho}{\mu}$

where L is the length of the test section measured in inches, v is fluidvelocity in ft/sec, ρ is the fluid density in lb/gal, D is the internaldiameter of the pipe measured in inches, Q is volumetric flow ingals/min, f is the Fanning friction factor, Re is Reynolds number, and μis dynamic viscosity of the liquid in cP. The units for differentialpressures are psi.

Core Permeability Testing

The impact of samples on core permeability was evaluated with aFormation Response Tester (FRT) using the following method. First, a 2inch long, 1 inch diameter section is cut out of an Ohio sandstone corewith a permeability around 1 milliDarcy (mD) using a lapidary trim saw.The cut core is then washed with water and dried overnight at 230° F.The wash water is preferably around 2.0% KCl so as to not damage claysthat may be present in the core. Diameter and length of the core aremeasured with a caliper. The core is then deaerated under vacuum at28-30 inches of mercury (in Hg) for 2 hours and saturated with 7% KClbrine overnight. The saturated core is then placed in the core holderchamber of the FRT instrument, at room temperature. The core chamber issubjected to 1500 psi confining pressure and 500 psi back pressure.Permeability of the core is measured in production this permeability istaken as the initial permeability value, K_(i). After production flowhas been stopped, 1 gallon of 0.166 volume % solution of thedrag-reducing additive in 7% KCl brine is flowed across the end of thecore at a flow rate of 0.8 L/min for 30 minutes under the applied 100psi pressure gradient. After the solution containing the drag-reducingadditive has been pumped for 30 minutes, the core is again flooded inproduction direction using the same conditions as used in determininginitial permeability. Final permeability of the core, K_(f), isdetermined. The percentage of permeability regained due to the use ofthe samples is then calculated as

$\frac{K_{f}}{K_{j}} \times 100\; {\%.}$

Rheology Measurements

Rheological measurements were performed to characterize materials of thepresent invention using the AR-G2 rheometer with 40 mm 2° cone-and-plategeometry from TA instruments. In a typical experiment a sinusoidaloscillating strain was applied to a sample at a frequency of 1 Hz(ω=6.283 radians per s), and stress varied between 0.05 and 150 Pa.Details of rheological measurements and meaning of principal rheologicalparameters are known to those skilled in the art. Materials of thepresent invention, as well as the emulsion polymers of the prior art,can be characterized by a combination of elastic (G′) and viscous (G″)modulus. The magnitude of complex viscosity, η*, can be calculated as

${\eta^{*}} = \left\lbrack {\left( \frac{G^{''}}{\omega} \right)^{2} + \left( \frac{G^{\prime}}{\omega} \right)^{2}} \right\rbrack^{1/2}$

Example 1

In a beaker, 22.5 grams of an ethoxylated castor oil surfactant such asStepantex CO-30, available from Stepan Corporation, are mixed with 17.5grams of d-limonene. The mixture is stirred until clear amber-coloredsolution is obtained. To this mixture is added 60 grams of the polymerdescribed in Samples 1-1 through 1-3 below. The resulting mixture isthen stirred at 300 rpm until a homogeneous, flowable formulation isobtained. Friction reducing performance and effect on core permeabilityare then evaluated as described above. Within the teachings of thisexample, the following samples were prepared:

Sample 1-1: Drag-reducing additive in which the polymer is the anioniccopolymer emulsion of acrylamide sodium acrylate, such as Hychem AE853,available from Hychem, Inc. This sample had an elastic modulus G′=9.6Pa, viscous modulus G″=8.8 Pa, complex viscosity of 2.1 Pa s, and didflow easily. Both of these values were much lower than the correspondingvalues established for AE853 polymer, which had G′=237.4 Pa, G″=70 Pa,and |η*|=39.4 Pa s.

Sample 1-2: Drag-reducing additive in which the polymer is a nonionicpolyacrylamide emulsion. In a preferred embodiment, the polymer isHychem NE823, available from Hychem, Inc.

Sample 1-3: Drag-reducing additive in which the polymer is a cationiccopolymer emulsion of acrylamide and dimethylaminoethylacrylate methylchloride quarternary salt (DMAEA MCQ), such as Hychem CE335, availablefrom Hychem, Inc.

Table 1 summarizes the drag reduction performance of Samples 1-1 through1-3, as well as the performance of constituent conventional polymeremulsions used alone. The dosing of both the Samples and theconventional polymer emulsions is 1 gpt of the conventional polymeremulsion.

TABLE 1 % Friction % Friction Reduction in Reduction in 7% Sample Flowrate (gpm) Water KCl Brine Sample 1-1 Ramping 12 77 77  6 71 72 12 77 77Recirculation 10 (t = 0 min) 76 74 10 (t = 10 min) 76 76 Sample 1-2Ramping 12 78 77  6 55 68 12 61 67 Recirculation 10 (t = 0 min) 55 61 10(t = 10 min) 48 54 Sample 1-3 Ramping 12 77 79  6 72 74 12 78 77Recirculation 10 (t = 1 min) 77 75 10 (t = 10 min) 77 69 AE853 Ramping12 75 70  6 69 60 12 75 66 Recirculation 10 (t = 0 min) 76 64 10 (t = 10min) 76 62 NE823 Ramping 12 78 77  6 63 52 12 64 62 Recirculation 10 (t= 0 min) 58 57 10 (t = 10 min) 50 51 CE335 Ramping 12 78 62  6 73 64 1279 75 Recirculation 10 (t = 0 min) 77 72 10 (t = 10 min) 77 60

Table 1 illustrates that although all Samples are effective dragreducers, some are more preferable than others. As such, microemulsifiedpolymer systems made with anionic polymers are preferred over those madewith a nonionic or cationic polymers. Table 1 also illustrates thebenefit of using the Samples over conventional polymers. Table 1indicates a rapid decrease in the percent friction reduction achievedwith conventional drag reducing polymer emulsions upon transition fromwater to 7% KCl brine, while this is not the case with the Samples.Also, under equivalent conditions, the Samples yielded consistentlyhigher values of friction reduction than the corresponding polymeremulsions alone. The data in Table 1 also indicates that in brine,cationic drag reducing polymer Hychem CE335 had to be recirculated inthe loop for a substantial period of time until the optimum dragreduction of 75% was achieved, while the system of the present inventionbased on the same polymer achieved this high level of drag reductionimmediately.

Example 2

In a beaker, 20 grams of ethoxylated castor oil are mixed with 20 gramsof terpene. The mixture is stirred until clear amber-colored solution isobtained. To this mixture is added 60 grams of the copolymer describedin Sample 2-1, 2-2, or 2-3 below. The resulting mixture is then stirredat 300 rpm until a homogeneous, flowable formulation is obtained.Friction reducing performance and effect on core permeability are thenevaluated as described above. Within the teachings of this example, thefollowing samples were prepared:

Sample 2-1: A copolymer emulsion of acrylamide and sodium acrylate iscombined with ethoxylated castor oil surfactant and peppermint oilterpenes according to the procedure in Example 2 above. In a preferredembodiment, the copolymer emulsion is Hychem AE853, available fromHychem, Inc., and the ethoxylated castor oil surfactant is StepantexCO-30, available from Stepan Corporation. The peppermint oil terpene isavailable from GreenTerpene.com.

Sample 2-2: A copolymer emulsion of acrylamide and sodium acrylate iscombined with ethoxylated castor oil surfactant and eucalyptus oilterpenes according to the procedure in Example 2 above. In a preferredembodiment, the copolymer emulsion is Hychem AE853, available fromHychem, Inc., and the ethoxylated castor oil surfactant is StepantexCO-30, available from Stepan Corporation. The eucalyptus oil terpene isavailable from GreenTerpene.com.

Sample 2-3: A copolymer emulsion of and sodium acrylate is combined witha sorbitan monooleate surfactant and a terpene comprising d-limoneneaccording to the procedure in Example 2 above. In a preferredembodiment, the copolymer emulsion is Hychem AE853, available fromHychem, Inc., and the surfactant is TWEEN 80. The d-limonene isavailable from Florida Chemical Company.

Drag reduction performance of Samples 2-1 through 2-3 in 7% KCl brine issummarized in Table 2. The dosing of both the Samples and theconventional polymer emulsions is 1 gpt of the conventional polymeremulsion.

TABLE 2 % Friction Reduction in Sample Flow rate 7% KCl Brine Sample 2-1Ramping 12 77  6 73 12 77 Recirculation 10 (t = 0 min) 75 10(t = 10 min)74 Sample 2-2 Ramping 12 77  6 73 12 77 Recirculation 10 (t = 0 min) 7610 (t = 10 min) 74 Sample 2-3 Ramping 12 77  6 72 12 77 Recirculation 10(t = 0 min) 75 10 (t = 10 min) 74

Table 2 shows that Samples 2-1 through 2-3 caused a reduction infriction by more than 70% and were superior to drag reducing polymerAE853 used alone (Table 1).

The results of core permeability evaluation with systems of theinvention indicated that samples from both Table 1 and Table 2 yieldedregained permeability of greater than 74%. Sample 1-1, which is aparticularly preferred embodiment, yielded regained permeability of 97%.

Example 3

To 27.3 g of ethoxylated castor oil surfactant (Stepantex CO-30), 72.7 gof Hychem AE853 copolymer emulsion was added, and the mixture wasstirred to form Sample 3. Formulation of a paste-like, highly viscousmaterial was observed. The paste was loaded into a syringe and extrudedinto the base liquid to achieve a dose of 1 gpt based on polymeractives. This sample had an elastic modulus G′=234 Pa, viscous modulusG″=87 Pa, and complex viscosity |η*|=42 Pa s. This material was muchless flowable than both material of example 1-1 and prior art frictionreducer Hychem AE853, as indicated by significantly higher values of G′and |η*|.

TABLE 3 % Friction Reduction in Sample Flow rate 7% KCl Brine Sample 3Ramping 12 76  6 71 12 76 Recirculation 10 (t = 0 min) 75 10(t = 10 min)75

The compositions of the present invention can be used for aiding in therecovery of crude oil and natural gas from subterranean formations. Itis possible to use these compositions by a variety of means. Forexample, in one suitable embodiment, compositions of the presentinvention may be delivered to the use site as a single formulation. Tomake such formulation, it is possible to mix the components in anyorder. In the other suitable unlimited embodiment, the individualcomponents making compositions of this invention can be mixed “on thefly”. Other means of using the systems of this invention may include,but are not limited to pre-dissolving one or more components in thetreatment fluid or pre-blending two or more components prior to theaddition of a third one. In preferred embodiments, acceptable treatmentranges may include adding from about 0.01 gallons to 50 gallons ofdrag-reducing additive per 1,000 gallons of the aqueous treatment fluid.

It is clear that the present invention is well adapted to carry out itsobjectives and attain the ends and advantages mentioned above as well asthose inherent therein. While presently preferred embodiments of theinvention have been described in varying detail for purposes ofdisclosure, it will be understood that numerous changes may be madewhich will readily suggest themselves to those skilled in the art andwhich are encompassed within the spirit of the invention disclosed andclaimed herein.

It is claimed:
 1. A method comprising the steps of: preparing adrag-reducing additive by mixing a dispersion polymer with a surfactantand a solvent; forming a drag-reducing composition by combining thedrag-reducing additive with an aqueous treatment fluid; and injectingthe drag-reducing composition into a subterranean formation, a pipelineor a gathering line.
 2. The method of claim 1, wherein the step offorming the drag-reducing composition with the aqueous treatment fluidfurther comprises the step of adding the drag-reducing additive into theaqueous treatment fluid on-the-fly as the aqueous treatment fluid ispumped into the subterranean formation, the pipeline or the gatheringline.
 3. The method of claim 1, wherein the step of forming thedrag-reducing composition further comprises the step of adding thedrag-reducing additive to the aqueous treatment fluid before thedrag-reducing composition is pumped into the subterranean formation, thepipeline or the gathering line.
 4. The method of claim 1, wherein thestep of forming the drag-reducing composition further comprises addingfrom about 0.01 gallons to about 50 gallons of drag-reducing additiveper 1,000 gallons of the aqueous treatment fluid.
 5. The method of claim1, wherein the step of preparing the drag-reducing additive furthercomprises mixing 40-85% by weight of the dispersion polymer with 10-35%by weight of the surfactant with an HLB greater than about 8 and 5-30%by weight of the solvent.
 6. The method of claim 1, wherein the aqueoustreatment fluid comprises an acid.
 7. A method comprising the steps of:preparing a drag-reducing additive by mixing 40-85% by weight of adispersion polymer with 10-35% by weight of a surfactant with an HLBgreater than about 8 and 5-30% by weight of a solvent; forming adrag-reducing composition by combining the drag-reducing additive withan aqueous treatment fluid; and injecting the drag-reducing compositioninto a subterranean formation, a pipeline or a gathering line.
 8. Themethod of claim 7, wherein the step of forming the drag-reducingcomposition with the aqueous treatment fluid further comprises the stepof adding the drag-reducing additive into the aqueous treatment fluidon-the-fly as the aqueous treatment fluid is pumped into thesubterranean formation, the pipeline or the gathering line.
 9. Themethod of claim 7, wherein the step of forming the drag-reducingcomposition further comprises the step of adding the drag-reducingadditive to the aqueous treatment fluid before the drag-reducingcomposition is pumped into the subterranean formation, the pipeline orthe gathering line.
 10. The method of claim 7, wherein the step offorming the drag-reducing composition further comprises adding fromabout 0.01 gallons to about 50 gallons of drag-reducing additive per1,000 gallons of the aqueous treatment fluid.
 11. The method of claim 7,wherein the aqueous treatment fluid comprises an acid.